Developing device with double spiral blade and image forming apparatus

Abstract

A developer tank of a developing device is partitioned into a first conveyance path, a second conveyance path, a first communicating path and a second communicating path with a partition. A first developer conveying member that conveys a developer in a first developer conveying direction is provided in the first conveyance path. A second developer conveying member that conveys the developer in a second developer conveying direction is provided in the second conveyance path. In the first developer conveying member, a double spiral blade is provided on a downstream side in the first developer conveying direction from a first conveying blade of the first developer conveying member, the double spiral blade including an inner spiral blade that conveys the developer in a first direction and an outer spiral blade that conveys the developer in a second direction.

What is claimed is: 
     
       1. A developing device comprising:
 a developer tank that stores a developer; 
 a partition that partitions an internal space of the developer tank into a first conveyance path along a longitudinal direction of the partition, a second conveyance path opposing to the first conveyance path with the partition interposed therebetween, and first and second communicating paths communicating with the first conveyance path and the second conveyance path at both ends in the longitudinal direction of the partition; 
 a first developer conveying member that is provided in the first conveyance path, and has a first rotation shaft which rotates around an axial line thereof, and a first conveying blade provided around the first rotation shaft, the first developer conveying member conveying the developer stored in the developer tank in a first developer conveying direction along the axial line of the first rotation shaft with rotation motion of the first conveying blade following rotation of the first rotation shaft; 
 a second developer conveying member that is provided in the second conveyance path, and has a second rotation shaft which rotates around an axial line thereof, and a second conveying blade provided around the second rotation shaft, the second developer conveying member conveying the developer stored in the developer tank in a second developer conveying direction, which is opposite to the first developer conveying direction, along the axial line of the second rotation shaft with rotation motion of the second conveying blade following rotation of the second rotation shaft; 
 a double spiral blade that is provided facing the first communicating path on a downstream side from the first conveying blade of the first developer conveying member in the first developer conveying direction, and comprises an inner spiral blade that is provided around the first rotation shaft of the first developer conveying member and conveys the developer stored in the developer tank in a first direction among axial line directions of the first rotation shaft with rotation motion following rotation of the first rotation shaft, and an outer spiral blade that is provided around the inner spiral blade and conveys the developer stored in the developer tank in a second direction among the axial line directions; and 
 a developing roller that bears and conveys the developer, 
 wherein the first developer conveying member is configured so that the first developer conveying direction is a same direction as the first direction, and 
 wherein the inner spiral blade is a cone-shaped general spiral blade whose internal diameter is constant and external diameter becomes continuously smaller as advancing in the first direction, and the outer spiral blade is an annular general spiral blade whose external diameter is constant and internal diameter becomes continuously larger as advancing in the second direction. 
 
     
     
       2. The developing device of  claim 1 , wherein the first developer conveying member is configured so that a rotation direction of the first rotation shaft of the first conveying member, when viewed in the first developer conveying direction, is a right-handed direction when a direction of a flow of the developer stored in the developer tank is a right-handed direction in a case of being viewed from a vertically upper side of the developer tank, and a left-handed direction when a direction of a flow of the developer stored in the developer tank is a left-handed direction in a case of being viewed from a vertically upper side of the developer tank. 
     
     
       3. The developing device of  claim 1 , wherein the outer spiral blade is formed of an elastic sponge. 
     
     
       4. An electrophotographic image forming apparatus comprising the developing device of  claim 1 . 
     
     
       5. A developing device comprising:
 a developer tank that stores a developer; 
 a partition that partitions an internal space of the developer tank into a first conveyance path along a longitudinal direction of the partition, a second conveyance path opposing to the first conveyance path with the partition interposed therebetween, and first and second communicating paths communicating with the first conveyance path and the second conveyance path at both ends in the longitudinal direction of the partition; 
 a first developer conveying member that is provided in the first conveyance path, and has a first rotation shaft which rotates around an axial line thereof, and a first conveying blade provided around the first rotation shaft, the first developer conveying member conveying the developer stored in the developer tank in a first developer conveying direction along the axial line of the first rotation shaft with rotation motion of the first conveying blade following rotation of the first rotation shaft; 
 a second developer conveying member that is provided in the second conveyance path, and has a second rotation shaft which rotates around an axial line thereof, and a second conveying blade provided around the second rotation shaft, the second developer conveying member conveying the developer stored in the developer tank in a second developer conveying direction, which is opposite to the first developer conveying direction, along the axial line of the second rotation shaft with rotation motion of the second conveying blade following rotation of the second rotation shaft; 
 a double spiral blade that is provided facing the first communicating path on a downstream side from the first conveying blade of the first developer conveying member in the first developer conveying direction, and comprises an inner spiral blade that is provided around the first rotation shaft of the first developer conveying member and conveys the developer stored in the developer tank in a first direction among axial line directions of the first rotation shaft with rotation motion following rotation of the first rotation shaft, and an outer spiral blade that is provided around the inner spiral blade and conveys the developer stored in the developer tank in a second direction among the axial line directions; and 
 a developing roller that bears and conveys the developer, 
 wherein the first developer conveying member is configured so that the first developer conveying direction is a same direction as the second direction, 
 the inner spiral blade is a cone-shaped general spiral blade whose internal diameter is constant and external diameter becomes continuously smaller as advancing in the first direction, and 
 the outer spiral blade is an annular general spiral blade whose external diameter is constant and internal diameter becomes continuously larger as advancing in the second direction. 
 
     
     
       6. The developing device of  claim 5 , wherein the first developer conveying member is configured so that a rotation direction of the first rotation shaft of the first conveying member, when viewed in the first developer conveying direction, is a right-handed direction when a direction of a flow of the developer stored in the developer tank is a right-handed direction in a case of being viewed from a vertically upper side of the developer tank, and a left-handed direction when a direction of a flow of the developer stored in the developer tank is a left-handed direction in a case of being viewed from a vertically upper side of the developer tank. 
     
     
       7. The developing device of  claim 5 , wherein the outer spiral blade is formed of an elastic sponge. 
     
     
       8. An electrophotographic image forming apparatus comprising the developing device of  claim 5 .